We improved the centrifugal fan for the noise and fluid performance. The fan has the inducer that is unified to the main blade. The geometry of the inducer was obtained with the tuft method and is unique. The fluid turns from axis- to radial-direction in the inducer. The inlet angle and the chord length of the inducer vary in span position. The aerodynamic and noise characteristics of the impeller with inducer have been compared to one without inducer. The total pressure and the efficiency of the impeller with inducer are increased about 20% and 5% in all flow rate. Because the pressure rise occurs in the inducer. And the pressure loss at the inlet of the blade becomes very small. The influence of the leakage flow between the shroud and the bellmouth is restricted near the front shroud, and then the separation of the boundary layer is controlled. The wake width of the main blade becomes fairly small. The specific noise level, which presents the noise performance of the fan, can be reduced about 2–4dB in wide flow rate.

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